1. Field of the Invention
The present invention relates to electric barriers and, more particularly, to electric barriers for fish.
2. Description of Prior Art
For decades, a fishing technique known as electrofishing has been employed for the purpose of collecting fish in conjunction with scientific research projects and for commercial fishing purposes. Generally, such technique employs either an alternating current system or a direct current or pulsed direct current system. In an alternating current system, fish within the threshold value of field intensity are immobilized either through electronarcosis or electrotetanus. The immobilized fish are collected either through use of an underwater vacuum system (siphon) or by net handlers dipping for the fish. Very often, a substantial percentage of the fish are immobilized below the electrodes and at a substantial depth where they are not retrievable. Moreover, a certain percentage of the dead or dying fish sink or are too far away to be retrieved. Because an alternating current system usually results in immediate or subsequent death of the fish, the system is seldom used for scientific studies involving inspection, tagging and release of the fish.
In a direct current or pulsed direct current system, the electrical field in proximity to the anode electrode will produce a neuromuscular twitch response in the fish which forces the fish to swim toward the anode electrode. The resulting concentration of fish in proximity to the anode electrode permits collection of the fish by an underwater vacuum (siphon) system or by net handlers netting the fish. Usually, the fish are not permanently injured or damaged by the field produced by the direct current or pulsed direct current.
One very serious problem with the direct current system is that related to electrolysis which results in a deposition of metallic oxides upon the cathode electrode. Such metallic oxides have electrical insulatng properties. The build up of such deposits will increasingly degrade the strength of the electrical field about the anode. A further detriment of the direct current system is that the electrical field strength produced is generally less than the electrical field strength produced by an alternating current system having the same power output. However, a pulsed direct current system appears to provide an electrical field strength commensurate with that of an alternating current system but still suffers from the other detriments of a direct current system.